Experiments are proposed to analyze the antiviral immune response in Pekin ducks infected with duck hepatitis B virus (DHBV) in order to define the roles of immunity, both in mediating liver damage in neonatally infected ducks and in preventing the establishment of persistent viremia in older infected ducks. The proposed analysis will involve the use of immunologically compromised ducks, selectively depleted of either B cells (bursectomy) or T cells (thymectomy) to determine the respective roles of these lymphoid cells in DHBV infection. In addition, as congenitally infected ducks do not exhibit liver pathology, the possibility will be investigated, by assays for immune reactivity to viral core and surface antigen, that these ducks are immunologically tolerant to viral antigen.